Likely has an air lock in the master cylinder.
Bench bleeding is usually recommended.
Remove line/s at master cylinder, hold finger over outlet/s and slowly press and release brake pedal, until fluid and no air force finger off. May need to remove finger while depressing pedal, then plug before releasing.
May need to lift front of kart to help get air from master cylinder.
After get airlock out of master, reconnect lines.
Open bleeder/s on caliper. With front still lifted, leave set for 30 minutes
Fluid should gravity into caliper.
If you still have trouble getting the last bit of air out, try leaving everything closed , front still lifted, depress pedal slightly, hold for short time, then release.
If you have cap off reservoir, you may see/ hear air bubble inside.
Repeat until see no more air.
These are the things that worked for me.